The present invention relates to an automatic under-cart type guided tractor comprised of a frame with a driving unit and driving wheels on the underside, which guided tractor is constructed in order to travel guided by a guide signal sent out from a guide element, such as a magnetic tape laid along a path on a floor surface in a factory or a warehouse, and to pull a cart provided with free wheels and loaded with goods, with the guided tractor located under a load-carrying platform of the cart.
Conventionally with an under-cart type guided tractor an undivided rigid plate-like frame is used and the driving wheels are attached at the center of the underside of the frame by a suspension mechanism using a plate spring, a coil spring or the like. The suspension mechanism prevents the driving wheels from losing contact with the floor surface, (the traveling path surface), due to irregularities in the surface, ensures appropriate surface friction, and thereby enables the under-cart type guided tractor to travel smoothly.
However, the suspension mechanism using such a plate spring, a coil spring or the like cannot cope with relatively large irregularities in the surface, such as slopes, waves or the like, although it can cope with small bumps on the floor surface.
Thus, the conventional under-cart type guided tractor has a problem, when, for example, the guided tractor passes over a convex portion of the floor surface, the surface friction increases, and when it passes over a concave portion of the floor surface, the surface friction decreases, thus the appropriate surface friction is not ensured. When these irregularities in the floor surface are relatively large, such as slopes, waves or the like, the cart and the tractor may become inclined at different angles, so that the bottom of the cart comes in contact with the top of the tractor, which hinders traveling.
In addition, in the conventional under-cart type guided tractor, an undivided rigid plate-like frame is used generally. Therefore, when the floor surface has large irregularities, there is, for example, a risk that when the tractor proceeds from a downward slope to an upward slope, the driving wheels are lifted from the floor surface, so that the tractor becomes uncontrollable. On the other hand, when the tractor proceeds from an upward slope to a downward slope, there is a risk that the distance between the sensor, which is usually placed at a front portion of the tractor as viewed from the perspective of the tractor""s traveling direction, and the guide element, such as a magnetic tape, increases, to the extent that the tractor becomes uncontrollable.
Thus, the object of the present invention is to provide an under-cart type guided tractor that has a frame capable of being bent, supported by a fulcrum, that can therefore travel smoothly even on a floor surface having large irregularities, such as slopes, waves or the like, without using a special suspension mechanism for the driving wheels or free wheels adapted to traveling on the floor surface along with the driving wheels, and that can draw a cart safely without the vertical load of the cart acting on the tractor at all.
An under-cart type guided tractor according to the present invention comprised of a frame provided with a driving unit including driving wheels on the underside, adapted to travel guided by a guide signal sent out from a guide element such as a magnetic tape laid along a traveling path on a floor surface, and to draw a cart provided with free wheels and loaded with goods, with the guided tractor located under a load-carrying platform of the cart.
The frame of the guided tractor has a height that allows the guided tractor to move under a frame of the cart, and a structure that does not allow the vertical load of the cart to act on the guided tractor. The frame of the guided tractor comprises at least two separate frame components that are arranged in line in the guided tractor""s travelling direction and joined by a pin in such a manner that the frame components are allowed to bend in an upward or downward fashion. The frame of the guided tractor is provided with free wheels that are adapted to travel on the floor surface along with the driving wheels. The frame components are equipped with a clamp mechanism capable of being raised and lowered, and the clamp mechanism is adapted to rise and clamp the frame of the cart when the guided tractor has come to an appropriate position under the frame of the cart. A sensor is provided at a portion suitable for detecting the guide signal sent out from the guide element such as a magnetic tape.
In the under-cart type guided tractor according to the present invention, the frame of the guided tractor may comprise two separate front and rear frame components. Each of the frame components is provided with free wheels on the left and right sides, and the free wheels are adapted to travel on the floor surface along with the driving wheels. The driving unit is located near the portion of the guided tractor that is adapted to form a bend in the frame. Sensors are provided at a front central portion of the front frame component and at a rear central portion of the rear frame component.
In the under-cart type guided tractor according to the present invention, the frame of the guided tractor may also be comprised of three separate front, middle and rear frame components. Each of the front and rear frame components is provided with free wheels on the left and right side, and the free wheels are adapted to travel on the floor surface along with the driving wheels. The middle frame component is equipped with a clamp mechanism. Steering driving units are provided as the driving units at the front and rear frame components, and sensors are provided in the front and back of each of the steering driving units.
The free wheels provided at the frame of the guided tractor and the cart may be spring casters.
The above-described under-cart type guided tractor according to the present invention can travel smoothly not only on a horizontal floor surface but also on a floor surface having large irregularities, such as slopes, waves or the like, even without using a special suspension mechanism for the driving wheels or the free wheels adapted to travel along with the driving wheels, and can draw a cart safely without the vertical load of the cart acting on the guided tractor at all.